Conventionally, a smart system has been known, which controls a vehicle by using wireless communication between a portable device carried by a user and an onboard apparatus. The smart system performs smart operation such as unlocking of a door or start-up of a vehicle driving apparatus, by the portable device receiving a request signal transmitted from the onboard apparatus and replying an answer signal to the vehicle from the portable device.
For the smart system, there is a concern of a relay attack in which a suspicious person causes a vehicle to perform the smart operation by indirectly implementing communication between the portable device and the onboard apparatus with a relay, and by performing code matching.
In contrast, a technique for a countermeasure to the relay attack is disclosed in Patent literature 1. In the technique disclosed in Patent literature 1, multiple reception antennas of a portable device receive signals from multiple transmission antennas of an onboard apparatus, which are respectively provided to different positions of the vehicle. A relay attack is determined from an intensity ratio of the received signals between respective reception antennas.
In the technique of Patent literature 1, it is necessary for the portable device to receive all of signals from the multiple transmission antennas of the onboard apparatus. Accordingly, the multiple transmission antennas of the onboard apparatus may need to be provided so that most of the transmission ranges of the transmission antennas overlap each other.
The inventors of the present application have found the following regarding a vehicle system and an onboard apparatus and a portable device that are included in the vehicle system implementing authentication by wireless communication.
It may be necessary to make the arrangement different from the arrangement of the transmission antennas in a typical smart system in order to provide the multiple transmission antennas in the vehicle so that most of the transmission ranges of the transmission antennas overlap each other. Since the arrangement needs to satisfy a condition that the transmission antennas are arranged to be acceptable in terms of appearance of the vehicle when changing the arrangement of the transmission antennas, the effort and the cost for satisfying this condition may increase.
In order for most of the transmission ranges of the respective transmission antennas provided to different positions of the vehicle to overlap each other, it may be necessary to significantly increase the antenna output of the transmission antenna, and thus the power consumption of the vehicle may increase.